The present application is based on Japanese Patent Application No. 2001-112456, which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a reflective type light-emitting diode (hereinafter abbreviated as xe2x80x9creflective type LEDxe2x80x9d) having a light source having a light-emitting element mounted on a lead forming a reflecting mirror, and a reflecting mirror provided in opposition to the light source. Incidentally, in this specification, an LED chip itself is referred to as xe2x80x9clight-emitting elementxe2x80x9d, an emitter including a resin package or an optical device such as a lens system having an LED chip mounted thereon is referred to as xe2x80x9clight sourcexe2x80x9d, and a light-emitting device having a light source mounted thereon is generically referred to as xe2x80x9clight-emitting diodexe2x80x9d or xe2x80x9cLEDxe2x80x9d.
2. Description of the Related Art
An example of a related-art reflective type LED will be described below with reference to FIG. 4. FIG. 4 is a vertically sectional view showing the overall configuration of the related-art reflective type LED. As shown in FIG. 4, in the reflective type LED 30, a pair of leads 33a and 33b are provided for supplying electric power to a GaAs light-emitting element 32 which is mounted on one 33a of the leads 33a and 33b. The light-emitting element 32 and the other lead 33b are bonded to each other by a wire 34. A reflecting mirror 35 made from an aluminum sheet excellent in linear reflectance and pressed into a concave shape is disposed in opposition to a light-emitting surface of the light-emitting element 32. The light-emitting element 32, part of the pair of leads 33a and 33b, the wire 34 and the reflecting mirror 35 are sealed with a transparent epoxy resin 36. A light-radiating surface 36a is formed on a back surface side of the light-emitting element 32.
The reflecting mirror 35 has a reflecting surface formed as a paraboloid of revolution with the light-emitting element 32 as a focal point. Accordingly, all components of light emitted from the light-emitting element 32 and reflected by the reflecting mirror 35 are reflected in a direction parallel to the axis of the paraboloid of revolution and radiated from the light-radiating surface 36a to the outside. In such a manner, the reflective type LED 30 is configured with high external radiating efficiency.
In the reflective type LED 30, however, the reflecting mirror 35 needs to have a solid angle of about 2xcfx80 steradian to the light-emitting element to keep the external radiating efficiency high. That is, the reflecting mirror 35 must be formed to have an end portion reaching the height of the light-emitting surface of the light-emitting element 32 in order to reflect light radiated substantially horizontally from the light-emitting surface of the light-emitting element 32. Therefore, the reflecting mirror 35 has to be disposed closely to the light-emitting element 32. There arises a problem that the degree of freedom for designing the reflecting mirror 35 is restricted.
It is therefore an object of the present invention to provide a reflective type light-emitting diode in which high external radiating efficiency can be obtained to increase the degree of freedom for designing a reflection mirror even in the case where an end portion of a reflecting mirror does not reach the height of a light-emitting surface of a light-emitting element.
(1) According to the invention, there is provided a reflective type light-emitting diode having: a light source including a light-emitting element, leads for supplying electric power to the light-emitting element, and a concave reflecting mirror provided around the light-emitting element; and a reflecting mirror provided in opposition to the light source.
In the reflective type LED configured as described above, the concave reflecting mirror is provided around the light-emitting element of the light source. Hence, light emitted from a light-emitting surface of the light-emitting element is not diffused horizontally but concentrated on a region within a predetermined extent from an axis perpendicular to the light-emitting surface. For this reason, all the reflecting mirror provided in opposition to the light source has to do is to reflect light irradiating the region within the predetermined extent from the axis perpendicular to the light-emitting surface. Hence, the end portion of the reflecting mirror need not reach the height of the light-emitting surface, so that the degree of freedom for designing the reflecting mirror can be increased while the reflecting mirror can be disposed to be far from the light source. Moreover, all components of light radiated from the light source can be substantially reflected by the reflecting mirror so as to be radiated to the outside with high external radiating efficiency.
In such a manner, there is provided a reflective type LED in which high external radiating efficiency can be obtained to increase the degree of freedom for designing the reflecting mirror even in the case where the end portion of the reflecting mirror does not reach the height of the light-emitting surface of the light-emitting element.
(2) According to the invention, there is provided a reflective type light-emitting diode of the configuration as defined in (1), wherein the reflecting mirror provided in opposition to the light source has a solid angle of not higher than 1.65xcfx80 steradian to the light source.
As described above, the concave reflecting mirror is provided around the light-emitting element of the light source. Hence, light emitted from the light-emitting surface of the light-emitting element is not diffused horizontally but concentrated on a region within an extent of about 80 degrees from an axis perpendicular to the light-emitting surface. For this reason, all the reflecting mirror provided in opposition to the light source has to do is to reflect light irradiating the region within the extent of about 80 degrees from the axis perpendicular the light-emitting surface. This extent of about 80 degrees corresponds to a solid angle of about 1.65xcfx80 steradian. Hence, the reflecting mirror may have a solid angle of not higher than 1.65xcfx80 steradian. Accordingly, the end portion of the reflecting mirror need not reach the height of the light emitting surface, so that the degree of freedom for designing the reflecting mirror can be increased while the reflecting mirror can be disposed to be far from the light source. Moreover, all components of light radiated from the light source can be substantially reflected by the reflecting mirror so as to be radiated to the outside with high external radiating efficiency.
In such a manner, there is provided a reflective type LED in which high external radiating efficiency can be obtained to increase the degree of freedom fort designing the reflecting mirror even in the case where the end portion of the reflecting mirror does not reach the height of the light-emitting surface of the light-emitting element.
(3) According to the invention, there is provided a reflective type light-emitting diode of the configuration as defined in (1) or (2), wherein the light source further includes a light-transmissive material for sealing the light-emitting element, part of the leads and the concave reflecting mirror and for forming a light-radiating surface on the light-emitting surface side of the light-emitting element.
In the reflective type LED configured as described above, the light-emitting element is sealed with the light-transmissive material, so that the light quantity emitted from the light-emitting element becomes about twice as large as that in the case where the light-emitting element is not sealed. As a result, the luminous intensity of the light source and, accordingly, the luminous intensity of the reflective type LED increase greatly. In addition, the light-radiating surface is formed on the light-emitting surface side of the light-emitting element, so that light emitted from the light-emitting element having an irradiation range limited by the concave reflecting mirror provided around the light-emitting element can be further controlled to limit the irradiation range. Accordingly, the degree of freedom for designing the reflecting mirror provided in opposition to the light source can be increased more greatly.
In such a manner, there is provided a reflective type LED in which the luminous intensity increases greatly while the degree of freedom for designing the reflecting mirror can be increased more greatly.
(4) According to the invention, there is provided a reflective type light-emitting diode of the configuration as defined in (3), wherein the light-radiating surface forms a convex lens.
In the reflective type LED configured as described above, the convex lens is formed on the light-emitting surface side of the light-emitting element. Hence, light emitted from the light-emitting element having an irradiation range limited by the concave reflecting mirror can be further condensed to narrow the irradiation range. Accordingly, the end portion of the reflecting mirror provided in opposition to the light source can be made farther from the light-emitting surface of the light-emitting element, so that the degree of freedom for designing the reflecting mirror can be increased more greatly.
In such a manner, there is provided a reflective type LED in which the range of irradiation with light from the light source can be made narrower to increase the degree of freedom for designing the reflecting mirror more greatly.
(5) According to the invention, there is provided a reflective type light-emitting diode of the configuration as defined in (3) or (4), wherein the light-radiating surface is shaped like an ellipsoidal convex lens having a top portion truncated into a flat surface.
In the configuration, among all components of light emitted from the light-emitting element having an irradiation range limited within the predetermined extent from the axis perpendicular to the light-emitting surface by the concave reflecting mirror, light components in the central portion around the axis perpendicular to the light-emitting surface are not radiated straightly as they are, but refracted outward and radiated obliquely. Accordingly, the central portion of the reflecting mirror disposed in opposition to the light source is scarcely irradiated with light. The light reflected from the central portion of the reflecting mirror is, however, blocked by the light source opposite to the reflecting mirror, so as not to be allowed to go out. Hence, wasteful light hitting on the central portion of the reflecting mirror can be substantially eliminated, so that light emitted from the light-emitting element can be reflected more effectively to improve the external radiating efficiency more greatly. In addition, even in the case where the size of the reflective type LED is reduced as a whole in this configuration, the external radiating efficiency can be kept high because the central portion of the reflecting mirror is scarcely irradiated with light. Hence, the size of the reflective type LED can be reduced.
In such a manner, there is provided a reflective type LED in which the degree of freedom for designing the reflecting mirror can be increased while greater improvement of external radiating efficiency and reduction in size can be achieved.
(6) According to the invention, there is provided a reflective type light emitting diode of the configuration as defined in anyone of (1) to (5), further having a light-shielding member including a light-transmission hole, wherein the reflecting mirror provided in opposition to the light source condenses light from the light source into the light-transmission hole of the light-shielding member so that the condensed light is radiated to the outside through the light-transmission hole.
Here, the xe2x80x9clight-transmission holexe2x80x9d maybe a through-hole or a hole filled with a light-transmissive material.
The reflective type LED according to the invention is a so-called light-shielding reflective type LED. The xe2x80x9clight-shielding reflective type LEDxe2x80x9d means a reflective type LED in which the size of a light-transmission hole provided in a light-shielding member is made the required smallest to prevent lowering of contrast between light at the time of turning on the light source and shade at the time of turning off the light source from being caused by external light which goes out again because the external light passes through the light-transmission hole and is reflected by the reflecting mirror. It is therefore necessary to form the reflecting surface of the reflecting mirror into a special shape in order to reflect and condense light from the light source efficiently to make the light pass through the light-transmission hole formed to have the required smallest size. Examples of the special shape of the reflecting surface include: a shape of an aggregate of parts of a plurality of spheroids each with the light source and the light-transmission hole as its focal points; and a shape in which a part of an ellipse with the light source and the light-transmission hole as its focal points is rotated around a central axis of the ellipse.
In the reflective type LED according to the invention, however, the concave reflecting mirror is provided around the light-emitting element to thereby increase the degree of freedom for designing the reflecting mirror provided in opposition to the light source. Hence, the reflective type LED can be provided as a light-shielding reflective type LED having high external radiating efficiency. Moreover, in the reflective type LED according to the invention, the reflecting mirror can be provided to be far from the light source, so that the directivity of light radiated from the light-transmission hole can be enhanced without any change of the positional relation between the light source and the light-transmission hole. Hence, the resulting light can be controlled easily by a secondary optical system provided on the outside, so that the reflective type LED can be formed as a light-shielding reflective type LED which is widely applicable.
In such a manner, there is provided a reflective type LED in which the directivity of light radiated from the light-transmission hole can be enhanced as well as the external radiating efficiency is high also as a light-shielding reflective type LED.
Features and advantages of the invention will be evident from the following detailed description of the preferred embodiments described in conjunction with the attached drawings.